A conventional flow control apparatus for a construction machine in accordance with the prior art as shown in FIG. 1 includes:
an engine 1;
a variable displacement hydraulic pump (hereinafter, referred to as “hydraulic pump”) 2 connected to the engine 1;
a first hydraulic cylinder 3 and a second hydraulic cylinder 4, which are connected to the hydraulic pump 2;
a first control valve 6 installed in a center bypass path 5 of the hydraulic pump 2, the first control valve being configured to allow hydraulic fluid discharged from the hydraulic pump 2 to be returned to a hydraulic tank T in its neutral state and configured to control a start, a stop, and a direction change of the first hydraulic cylinder 3 in its shifted state;
a second control valve 7 installed on a downstream side of the center bypass path 5 of the hydraulic pump 2, the second control valve being configured to allow the hydraulic fluid discharged from the hydraulic pump 2 to be returned to the hydraulic tank T in its neutral state and configured to control a start, a stop, and a direction change of the second hydraulic cylinder 4 in its shifted state; and
a regeneration flow path 10 configured to supplement and reuse the hydraulic fluid that returns to the hydraulic tank T from a large chamber of the first hydraulic cylinder 3 during a retractable drive of the first hydraulic cylinder 3 due to an attachment (including a boom, an arm, or a bucket)'s own weight, and a regeneration valve 13 installed in the regeneration flow path 10.
As shown in FIG. 1, when a spool of the first control valve 6 is shifted to the right on the drawing sheet by a pilot signal pressure from a pilot pump (not shown) through the manipulation of a manipulation lever (not shown), hydraulic fluid discharged from the hydraulic pump 2 is supplied to a small chamber of the first hydraulic cylinder 3 via a meter-in flow path 12 of the first control valve 6. In this case, hydraulic fluid discharged from a large chamber of the first hydraulic cylinder 3 is returned to the hydraulic tank T via the first control valve 6 and the return flow path 11. Thus, the first hydraulic cylinder 3 is driven to be retracted so that the boom can be driven to perform a boom-down operation.
In addition, when the spool of the first control valve 6 is shifted to the left on the drawing sheet through the manipulation of a manipulation lever (not shown), hydraulic fluid discharged from the hydraulic pump 2 is supplied to the large chamber of the first hydraulic cylinder 3 via the first control valve 6. In this case, hydraulic fluid discharged from the small chamber of the first hydraulic cylinder 3 is returned to the hydraulic tank T via the first control valve 6 and the return flow path 11a. Thus, the first hydraulic cylinder 3 is driven to be extended so that the boom can be driven to perform a boom-up operation.
Meanwhile, when the hydraulic fluid from the large chamber of the first hydraulic cylinder 3 is returned to the hydraulic tank T due to the retractable drive of the first hydraulic cylinder 3, a back pressure is formed in the regeneration flow path 10 by a back pressure check valve 18 installed in the return flow path 11. For this reason, when a pressure within the small chamber of the first hydraulic cylinder 3 is low, the hydraulic fluid returned from the large chamber of the first hydraulic cylinder 3 to the hydraulic tank T can be supplementarily supplied to the small chamber of the first hydraulic cylinder 3 through the regeneration flow path 10.
In other words, when there is a shortage in the hydraulic fluid supplied to the small chamber during the retractable drive of the first hydraulic cylinder 3, the hydraulic fluid returned from the large chamber of the first hydraulic cylinder 3 to the hydraulic tank T can be recycled and supplementarily supplied to the small of the first hydraulic cylinder 3 through the regeneration flow path 10.
In the meantime, when a combined operation of a boom and an arm is performed by a user, i.e., when the first hydraulic cylinder 3 is driven to be retracted to perform the boom-down operation of the boom and the second hydraulic cylinder 4 is driven to be retracted to perform the arm-out operation of the arm, a load pressure generated in the second hydraulic cylinder 4 is relatively higher than that generated in the first hydraulic cylinder 3. In this case, the hydraulic fluid discharged from the hydraulic pump 2 is much more supplied to the first hydraulic cylinder 3 whose load pressure is relatively low through the meter-in flow path 12 in terms of the characteristics of the hydraulic fluid.
In other words, the conventional flow control apparatus entails a problem in that since the hydraulic fluid discharged from the hydraulic pump 2 is much more supplied to the first hydraulic cylinder 3 through the meter-in flow path 12, the efficiency of the recycled hydraulic fluid is degraded. Besides, there is a problem in that the hydraulic fluid from the hydraulic pump 2 is introduced into the small chamber of the first hydraulic cylinder 3, which causes a loss of the hydraulic fluid, thus leading to a decrease in the energy efficiency of the machine.